News broke yesterday morning that eight people in London and the South East had been arrested on suspicion of trading stocks with inside knowledge – a notoriously difficult offence to prove.

The FSA said the arrests were part of an "ongoing investigation into insider dealing rings".

It has since been reported that the source of the leaks may have been the banks' printing plant, in a scam involving the leaking of confidential deal-related documents.

The Times reported this morning quoting "City sources" that "at least one printer" was among those arrested. The eight men have been released on bail and will face further questioning, the FSA said.

Earlier this year, Japanese financial authorities investigated a Tokyo-based printer on similar charges.

More to follow…